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Dark Fiber, also written as “Dark Fibre,” is fiber optic cable, and the associated infrastructure, that is buried underground, but has no data flowing through it. Because fiber-optic cables send data through beams of light, the fiber is considered dark when it is unused.

The cost of cabling infrastructure is very high. But, a very small portion of that cost is the fiber itself. The vast majority of the cost goes into obtaining the necessary permits, and the cost of the labor of laying the cables. In fact, compared to copper, which is often stolen, fiber optic cable is practically worth nothing. It is in the best interest of telecommunications companies to lay down much more fiber optic cable than they need, expecting to lease the fiber to other telephone, cable, or internet providers.

In the period leading up to the crash of 2000, now called “the dot-com bubble,” investors were eager to pour money into internet companies. Because of all the bandwidth that would be required by all these soon-to-be-the-next-Yahoos, investment in fiber-optic cable seemed a very sound bet. Unfortunately, it wasn’t. Many of the companies that invested in the fiber even went bankrupt after the cable was already buried. Now, telecom companies are buying up this unused fiber and either using it in-house or leasing it out. In 2005, Google started buying up dark fiber all around the country, and we now know that this will likely be the foundation for Google Fiber.

Because there is so much dark fiber available, the cost of fibre-optic bandwith has gone down significantly. According to many experts, the rights to a mile of dark fibre can be had for under $200, compared to over $1,200 for a mile before dark fibre. Many organizations, including both for-profit telecommunications companies and educational institutions, purchase enough fibre to create their own private backbone network.